Peptidergic and cholinergic neurons and mediators in peptone-induced gastroprotection: role of cyclooxygenase-2

Heat-Stress Preconditioning Attenuates Behavioral Responses to Psychological Stress: The Role of HSP-70 in Modulating Stress Responses

Exposure to high ambient temperature is a stressor that influences both biological and behavioral functions and has been previously shown to have an extensive impact on brain structure and function. Physiological, cellular and behavioral responses to heat-stress (HS) (40-41 °C, 2 h) were evaluated in adult male Sprague-Dawley rats. The effect of HS exposure before predator-scent stress (PSS) exposure (i.e., HS preconditioning) was examined. Finally, a possible mechanism of HS-preconditioning to PSS was investigated. Immunohistochemical analyses of chosen cellular markers were performed in the hippocampus and in the hypothalamic paraventricular nucleus (PVN). Plasma corticosterone levels were evaluated, and the behavioral assessment included the elevated plus-maze (EPM) and the acoustic startle response (ASR) paradigms. Endogenous levels of heat shock protein (HSP)-70 were manipulated using an amino acid (L-glutamine) and a pharmacological agent (Doxazosin). A single exposure to an acute HS resulted in decreased body mass (BM), increased body temperature and increased corticosterone levels. Additionally, extensive cellular, but not behavioral changes were noted. HS-preconditioning provided behavioral resiliency to anxiety-like behavior associated with PSS, possibly through the induction of HSP-70. Targeting of HSP-70 is an attractive strategy for stress-related psychopathology treatment.

COX-1, COX-2 and the topical effect in NSAID-induced enteropathy

The side effects of NSAIDs are equally evident in the stomach and the small bowel. The latter is increasingly seen as being clinically significant, contributing substantially to the iron-deficiency anaemia that is so common in patients with rheumatoid arthritis. Furthermore, NSAID-enteropathy may be associated with life-threatening events. The pathogenesis of NSAID-enteropathy is uncertain but inhibition of COX-1 is believed to be of pivotal importance. However there is increasing evidence that COX-2 inhibition and the topical effect may have a synergistic detrimental action. We examined the role of COX-1, COX-2 and the so called topical effect of acidic NSAIDs. We found that COX-1 or COX-2 inhibition and the topical effect alone do not damage the GI tract. Dual inhibition of COX-1 and COX-2 results in intestinal inflammation similar to that caused by Indomethacin. The topical effect may act synergistically in this damage. The conventional view that the mechanism of gastrointestinal damage is principally caused by COX-1 inhibition needs to be revised in view of recent studies using selective inhibitors of the COX enzymes and COX knockout animals.

Gastrin enhances gastric mucosal integrity through cyclooxygenase-2 upregulation in rats

Gastrin, PGs, and growth factors have important roles in maintaining gastrointestinal mucosal integrity. Cyclooxygenases (COX-1 and COX-2) are the key enzymes involved in PG synthesis. This study aimed to clarify the mechanisms of gastric mucosal protection by gastrin. Fasted rats were administered subcutaneous gastrin 17 with or without gastrin receptor antagonist YM022 pretreatment. Heparin-binding epidermal growth factor-like growth factor (HB-EGF) and COX-2 expression were examined using Western blot analysis. Another series of experiments investigated 1) PGE(2) levels in gastric mucosa, 2) the protective action of gastrin against gastric damage by acidified ethanol, 3) the effects of a specific HB-EGF-neutralizing antibody on gastrin-induced COX-2 expression, and 4) the effects of a specific COX-2 inhibitor NS-398 on PGE(2) synthesis and the mucosal protection afforded by gastrin. Gastrin dose-dependently increased HB-EGF, COX-2 expression, and PGE(2) levels and reduced gastric damage. However, pretreatment with YM022 dose-dependently abolished such effects of gastrin. A specific HB-EGF- neutralizing antibody and an EGF receptor inhibitor decreased gastrin-induced COX-2 expression. NS-398 blocked gastrin-induced PGE(2) synthesis and mucosal protection. In conclusion, this study demonstrates that gastrin enhances gastric mucosal integrity through COX-2, which is partially mediated by HB-EGF, and PGE(2) upregulation in rats.

Effects of specific inhibition of cyclo-oxygenase-1 and cyclo-oxygenase-2 in the rat stomach with normal mucosa and after acid challenge

1. Effects of the cyclo-oxygenase (COX)-1 inhibitor SC-560 and the COX-2 inhibitors rofecoxib and DFU were investigated in the normal stomach and after acid challenge. 2. In healthy rats, neither SC-560 nor rofecoxib (20 mg kg(-1) each) given alone damaged the mucosa. Co-treatment with SC-560 and rofecoxib, however, induced severe lesions comparable to indomethacin (20 mg kg(-1)) whereas co-administration of SC-560 and DFU (20 mg kg(-1) each) had no comparable ulcerogenic effect 5 h after dosing. 3. SC-560 (20 mg kg(-1)) inhibited gastric 6-keto-prostaglandin (PG) F(1alpha) by 86+/-5% and platelet thromboxane (TX) B(2) formation by 89+/-4% comparable to indomethacin (20 mg kg(-1)). Rofecoxib (20 mg kg(-1)) did not inhibit gastric and platelet eicosanoids. 4. Intragastric HCl elevated mucosal mRNA levels of COX-2 but not COX-1. Dexamethasone (2 mg kg(-1)) prevented the up-regulation of COX-2. 5. After acid challenge, SC-560 (5 and 20 mg kg(-1)) induced dose-dependent injury. Rofecoxib (20 mg kg(-1)), DFU (5 mg kg(-1)) and dexamethasone (2 mg kg(-1)) given alone were not ulcerogenic but aggravated SC-560-induced damage. DFU augmented SC-560 damage 1 but not 5 h after administration whereas rofecoxib increased injury after both treatment periods suggesting different time courses. 6. Gastric injurious effects of rofecoxib and DFU correlated with inhibition of inflammatory PGE(2). 7. The findings show that in the normal stomach lesions only develop when both COX-1 and COX-2 are inhibited. In contrast, during acid challenge inhibition of COX-1 renders the mucosa more vulnerable suggesting an important role of COX-1 in mucosal defence in the presence of a potentially noxious agent. In this function COX-1 is supported by COX-2. In the face of pending injury, however, COX-2 cannot maintain mucosal integrity when the activity of COX-1 is suppressed.

Selective cyclo-oxygenase-2 inhibitors aggravate ischaemia-reperfusion injury in the rat stomach

1. Effects of indomethacin, the selective cyclo-oxygenase (COX)-2 inhibitors NS-398 and DFU, and dexamethasone on gastric damage induced by 30 min ischaemia followed by 60 min reperfusion (I-R) were investigated in rats. Modulation of gastric levels of COX-1 and COX-2 mRNA by I-R was evaluated using Northern blot and reverse transcription-polymerase chain reaction. 2. I-R-induced gastric damage was dose-dependently aggravated by administration of indomethacin (1 - 10 mg kg(-1)), NS-398 (0.4 - 4 mg kg(-1)) or DFU (0.02 - 2 mg kg(-1)) as assessed macroscopically and histologically. 3. Likewise, administration of dexamethasone (1 mg kg(-1)) significantly increased I-R damage. 4. Low doses of 16, 16-dimethyl-prostaglandin(PG)E(2), that did not protect against ethanol-induced mucosal damage, reversed the effects of the selective COX-2 inhibitors, indomethacin and dexamethasone. 5. I-R had no effect on gastric COX-1 mRNA levels but increased COX-2 mRNA levels in a time-dependent manner. Dexamethasone inhibited the I-R-induced expression of COX-2 mRNA. 6. I-R was not associated with a measurable increase in gastric mucosal formation of 6-keto-PGF(1alpha) and PGE(2). PG formation was substantially inhibited by indomethacin (10 mg kg(-1)) but was not significantly reduced by NS-398 (4 mg kg(-1)), DFU (2 mg kg(-1)) or dexamethasone (1 mg kg(-1)). 7. The findings indicate that selective COX-2 inhibitors and dexamethasone markedly enhance gastric damage induced by I-R. Thus, whereas COX-2 has no essential role in the maintenance of gastric mucosal integrity under basal conditions, COX-2 is rapidly induced in a pro-ulcerogenic setting and contributes to mucosal defence by minimizing injury. This suggests that in certain situations selective COX-2 inhibitors may have gastrotoxic effects.